[Eeglablist] multiple runs/parts of the same paradigm - when to concatenate

[Stephen Politzer-Ahles]

Hi Janosch,

Actually I had misread your previous message.... in your case it is
probably fine to run ICA on the concatenated data, since the cap wasn't
taken off in between blocks. The time when you'd want to do ICA before
concatenation is when the cap was taken off in between (e.g., if you
divided experimental sessions over two different days), because small
differences in the cap's placement can cause the same physiological
"component" to appear as two different ICs. But it sounds like your blocks
are from the same recording 'session', with the cap staying on the whole
time, so this is probably not an issue. Since that's not an issue, then
like Iman said, it's ideal to have as many samples as possible for your ICA.

Best,
STeve



Stephen Politzer-Ahles
New York University, Abu Dhabi
Neuroscience of Language Lab
http://www.nyu.edu/projects/politzer-ahles/


On Wed, Apr 9, 2014 at 10:32 AM, Janosch Linkersdörfer <
notes4januz at gmail.com> wrote:

> Hi Steve and Iman,
>
> thank you very much for your answers. I indeed plan on using ICA for
> preprocessing. As you propose different strategies (concatenating before
> vs. after ICA), could you please elaborate on why it is or is not
> appropriate. Could you maybe point me to some literature?
>
> Thanks a lot,
>
> Janosch
>
> >> I would prefer to concatenate all and then do ICA and etc , especially
> if your data sampleas are few...
> >> Best
> >> Iman
> >>
> >> ============================================
> >> Iman M.Rezazadeh, Ph.D , M.Sc., B.Sc.
> >> Semel Institute for Neuroscience and Human Behavior
> >> University of California, Los Angeles (UCLA)
> >> Am 09.04.2014 um 06:22 schrieb Stephen Politzer-Ahles <
> politzerahless at gmail.com>:
>
> > Hi Janosch,
> >
> > This depends on what things you are doing during preprocessing. For
> example, if you are doing ICA, then this should be done before
> concatenation. For many other steps, like epoching and filtering, this
> doesn't really matter (although a filter might take longer to run on the
> concatenated than the un-concatenated data, since it would have to deal
> with the boundary).
> >
> > Best,
> > Steve
> >
> >
> >
> > Stephen Politzer-Ahles
> > New York University, Abu Dhabi
> > Neuroscience of Language Lab
> > http://www.nyu.edu/projects/politzer-ahles/
> >
> >
> > On Tue, Apr 8, 2014 at 6:18 PM, Janosch Linkersdörfer <
> notes4januz at gmail.com> wrote:
> > Hi all,
> >
> > I am writing a script to import EGI .mff data into eeglab and save them
> as .set files for further (pre)processing.
> >
> > One of the paradigms is split into two runs. For another paradigm that
> should have been run in one go, for some of the participants there are two
> files, because the participants (children) had to go to the bathroom in
> between blocks.
> >
> > In the script I look whether multiple files for one paradigm exist, and
> if so concatenate them using pop_mergeset.
> >
> > I now wonder whether this is correct or whether I instead have to
> preprocess each file individually and later concatenate them before (or
> after) epoching.
> >
> > It would be great if you could help me!
> >
> > Thanks,
> >
> > J
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